The present invention relates to a pointing device for supporting and pointing loads or components in a determined position. More particularly, the invention relates to precision pointing devices for placing in unstable environments that impart vibrations or multiple movements to such systems. In addition, the invention also relates to pointing systems on board space vehicles such as those used in satellites, exploration modules, or space probes.
In numerous fields, and in particular in the aerospace, detection, or telecommunications fields, some of the components used need to be pointed or steered with great accuracy. The loads or components concerned are any type of apparatus that needs to be accurately pointed in order to operate. By way of example, such components can be plasma thrusters for correcting the position of a satellite in orbit, transceiver antennas, mirrors, . . . In such applications, the components are associated with a pointing device or mechanism which is designed to support the components and to place them in a determined position. A component and its pointing mechanism once in association form an assembly which implements both the pointing function and the function of the component.
By way of example, when pointing plasma thrusters for correcting satellite orbits or when pointing satellite antennas, the range of values over which the entire component and pointing mechanism assembly can move is of the order of a few degrees. Thus, the reliability of the mechanisms both in terms of strength and in terms of precision determines whether or not the components they support operate properly.
Two problems arise with onboard components, i.e. components which need to be transported to the site at which they are to operate, e.g. those used in satellites that need to be placed in orbit by means of a rocket. Firstly, during transport, the pointing mechanism which supports the component must be capable of holding the component in a safe position while also guaranteeing proper mechanical behavior for protecting the component as far as possible against the significant stresses and vibrations due to accelerations. Secondly, the pointing mechanism must then be capable of becoming operational, i.e. the mechanism must have retained a predetermined orientation or must be capable of being moved so as to point the component into a determined position.
Concerning components that need to operate during transport or in an environment that is highly disturbed (vibration, impact, acceleration, . . . ), the two above-identified problems amount to a single problem. Under such circumstances, the system must be capable of protecting the component as much as possible from the mechanical disturbances generated by its conditions of use while simultaneously ensuring that the component is pointed precisely.
Considering such problems, numerous pointing systems have been devised, however they generally present mechanical structures that are very complicated, thereby significantly increasing the mass and the cost of the assembly to be transported or to be used without genuinely protecting the supported component from shock or vibration during transport or in operation.
Amongst known pointing systems, there are mechanisms making use of cardan mounts or of shafts. Those systems suffer from a major drawback associated with the hinge elements used. Cardan mounts or shafts as used in such systems cannot hold the component stably, and they transfer a large amount of vibration to the component during transport. In order to keep the assembly in a stable position during transport, solutions involving locking the pointing system have been considered. By way of example, they consist in a device of the kind described in xe2x80x9cHigh performance reactionless scan mechanismxe2x80x9d, by E. I. William, R. T. Summers, M. A. Ostaszewski, Ball Aerospace, 29th Aerospace Mechanism Symposium, NASA Conference Publication 3293, which device presents a pointing mechanism with cardan mounts that are xe2x80x9clockedxe2x80x9d via the actuators for launch purposes. Nevertheless, in such a mechanism, the cardan mounts are prevented from moving only via the actuators which leaves the cardan mounts with a certain amount of slack that is sufficient for transmitting undesirable vibration to the load.
Another solution, described in the document xe2x80x9cThruster orientation mechanismxe2x80x9d, by S. Mankai, Alcatel Space Industries, 8th European Space Mechanisms and Tribology Symposium, ESA SP-438, consists in a plasma thrust pointing system which comprises two plasma thrusters disposed on a common plate carried by silicone dampers and a two-axis cardan mount fitted with ball bearings. That system is pointed by linear actuators placed on roller screws. The entire mechanical structure of that system is locked by an assembly of holding plates and bolts fitted with apparatus including pyrotechnical cutters for releasing the assembly on its site of operation. That solution is unsatisfactory since shocks due to the pyrotechnical devices are undesirable on sensitive components such as plasma thrusters. In addition, the system is very heavy, having a mass of 17 kilograms (kg) even though the maximum mass required for that type of system in a plasma thrust application for a satellite is no more than 8 kg. Finally, apart from its large mass, that system continues to be highly vibratory.
The present invention seeks to remedy the above-mentioned drawbacks and to provide a pointing device that is simple and capable, in a single structure, of combining the functions of stabilization and of pointing.
These objects are achieved by means of a pointing device for supporting a load on a support element, the load being supported above the support element by moving link means, wherein the moving link means comprise at least three distinct link arms distributed around the load, each link arm comprising a flexible element having a first end connected to the support element via a first hinge having a single degree of freedom, and a second end connected to the load via a second hinge having a single degree of freedom, and wherein the pointing device further comprises at least one means for transmitting movement disposed between the support element and the load to point the load relative to the support element.
The device of the invention thus makes it possible to connect a load to a support element via backlash-free links, thus giving additional stiffness to the assembly while conserving a certain amount of mobility for pointing.
In a particular aspect of the invention, the load also comprises a fixing bracket connected to the link arms.
In an aspect of the invention, in each link arm, the first hinge has a first pin supporting the first end of the flexible element, the first pin being fixed to the support element by a fixing member, and the second hinge comprises a second pin supporting the second end of the flexible element, the second pin being fixed to the load by a fixing member, the first and second pins of each link arm being parallel to each other and perpendicular to the flexible element when the device is in its initial position.
Thus, by means of these hinges assembled to each of its ends, and because of the flexible element which is connected to said hinges, each link arm retains stiffness necessary for supporting the load while nevertheless remaining movable in various directions so as to allow the supported load to be pointed in a determined direction.
According to a characteristic of the invention, the movement transmission means comprises an actuator formed by a stator element fixed to the support element, the stator element supporting a turntable having a retaining element fixed eccentrically on the turntable and having attached thereto a first ball-and-socket joint disposed at one end of a connecting rod, a second ball-and-socket joint disposed at the opposite end of the connecting rod being attached to a retaining element disposed on the supported load, the first and second ball-and-socket joints provided at the ends of the connecting rod being free to rotate about their respective retaining elements.
With this type of actuator, the device can be pointed in numerous directions without the actuator being directly connected thereto, thus avoiding increasing the weight of the load and avoiding transmitting additional vibration thereto.
According to another characteristic of the invention, the movement transmission means comprises an actuator formed by a stator element fixed to the support element, the stator element supporting a turntable having a first hinge with a single degree of freedom fixed eccentrically on the turntable and connected to a first end of a flexible element, the second end of the flexible element being connected to the load via a second hinge having a single degree of freedom.
The stiffness of the device as a whole can be further increased by making backlash-free links for the movement transmission means in this way.
In an aspect of the invention, the stator element comprises a motor for positioning the turntable.
The device can thus point the load it supports as a function of control relationships applied to the actuators.
In another aspect of the invention, the stator element comprises a mechanism for driving the turntable, the mechanism being irreversible.
With such an irreversible mechanism, the load can be held in a predetermined orientation without the actuators being powered.
In an aspect of the invention, the flexible element comprises a laminated structure made up of a stack of a plurality of laminations.
Such a structure provides a compromise between the flexibility and the stiffness required by each flexible element to ensure the load support is stable and capable of being pointed.
More particularly, each of the laminations of the plurality of laminations comprises a metal lamination covered in a resilient material.
Thus, the presence of metal in the laminations ensures that each flexible element is stiff, with contact flexibility between the laminations being obtained by the elastic coating material.
Specifically, the metal constituting the lamination is stainless steel and the resilient covering material is vulcanized rubber or silicone compression-bonded onto the metal.
For use in air, it is preferable to use vulcanized rubber, whereas for use in a vacuum, silicone is more suitable.
More particularly, the device comprises two movement transmission means disposed in two distinct directions.
The load can then be pointed through two angles of inclination.
In an embodiment of the invention, the moving link means comprise four link arms disposed uniformly around the supported load.
The device constituted in this way advantageously constitutes the beginning of a square-based pyramid structure on which the load is supported.
In another embodiment of the invention, the moving link means comprise five link arms distributed uniformly around the supported load.
The device constituted in this way advantageously forms the beginning of a pentagon-based pyramid structure on which the load is supported.
In a particular aspect, the support element is a portion of the external structure of an apparatus.
Still in a particular aspect of the invention, the load comprises a plasma thruster, an antenna, a light emitter, or a light receiver.
The device of the invention makes it possible to support and point loads constituted by fragile elements even in unstable environments.
The present invention also provides a pointing system comprising a plurality of pointing devices as described above, the devices being placed side by side and two adjacent devices using at least one movement transmission means in common.
The devices are thus pointed in series by common movement transmission means on which the forces exerted via the connecting rods come into balance.
The invention also provides a system on board a launcher, the system comprising apparatus with at least one load supported by a pointing device as described above.
Consequently, the device of the invention provides a solution that is inexpensive and reliable for launching space vehicles fitted with loads containing elements that are sensitive to vibration and acceleration of any kind.